Short answers, pulled from the story.
Selim III was the sultan of the Ottoman Empire from 1789 to 1807, known for his military reform program called the Nizam-i Cedid. He was deposed on the 29th of May 1807 by Janissaries who objected to his European-style military reforms, his confiscation of traditional land grants to fund the new army, and what they characterized as disrespect for Islamic tradition. They replaced him with his cousin Mustafa IV.
The Nizam-i Cedid, meaning New Order, was a reformed infantry corps established in 1797 and composed of Turkish peasant youths from Anatolia, trained and officered by Europeans using French-style uniforms and modern weapons. By 1806 the force numbered around 23,000 troops, including a modern artillery corps. Selim was unable to integrate it with the existing Ottoman army, limiting its effectiveness.
Selim III was murdered on the 28th of July 1808 inside the seraglio on the orders of Mustafa IV, who feared a loyalist army was marching on Constantinople to reinstate him. The assassins included the Master of the Wardrobe, Fettah the Georgian, the Treasury steward Ebe Selim, and a black eunuch named Nezir Ağa. His last words were "Allahu Akbar." He was the only Ottoman sultan killed by a sword.
Selim III created fourteen makams, the melodic types foundational to Turkish classical music, three of which remain in use today. Sixty-four compositions attributed to him survive, some still performed in the Turkish classical repertory. He commissioned the Hamparsum notation system, which became the dominant system for Turkish and Armenian music, and in 1797 hosted the first opera performance ever held in the Ottoman Empire.
At British request, Selim III wrote to Tipu Sultan urging him to cease hostilities against the British East India Company and offering Ottoman mediation. Tipu Sultan replied twice rejecting the advice. Before his letters could reach Constantinople, the Fourth Anglo-Mysore War had begun and Tipu Sultan was killed during the Siege of Seringapatam in 1799.
Selim III was buried in the Laleli Mosque, near the tomb of his father Sultan Mustafa III. The two consorts present during his assassination on the night of the 28th of July 1808 were Refet Kadın, born in 1777, and Pakize Hanım. Pakize threw herself between the assassins and Selim and was wounded in the hand; Refet threw herself on his body after he was killed and had to be dragged away.